The present invention relates to a novel reflective-type diffraction grating structure useful in the manufacturing of color display devices. More specifically, the present invention relates to an improved color display device containing a novel reflective-type diffraction grating. The utilization of the novel reflective-type diffraction grating structure allows the color display device to operate without the need for color filters, as required in prior art color display devices. As result, the color display device of the present invention substantially improves the brightness of the displayed images, and reduces the amount of power consumption. The novel design of the reflective-type diffraction also allows a black shading matrix to be generated between the RGB color components for improved contrast in the images.
With the wide proliferation of mobile consumer electronic devices such as cell phones, personal digital assistants (PDAs), etc, the need for associated parts, such as non-CRT-type flat panel displays with improved quality, also substantially increases. Liquid crystal displays (LCDs) are the most common types of non-CRT-type flat panel displays used in mobile communication devices.
Good brightness and low power consumption are two of the most important considerations in any display devices. These considerations become even more critical for LCD type plat panel displays commonly used in mobile communication devices. Brightness can greatly affect the visualizability of the mobile device. And manufacturers of mobile communication devices often have to make comprises between brightness and power consumption.
For conventional LCDs, color filters often constitute the largest share of the manufacturing cost, followed, in the order of their share of the manufacturing cost, by the electric driving-circuits and back-light assembly. Although the color filters function to allow light of a pre-defined color to pass therethrough, some absorption is inevitable, resulting in a loss in the intensity of the transmitted light.
U.S. Pat. No. 5,619,356 discloses a typical reflective-type liquid crystal display device. It include a first substrate, a second substrate, a liquid crystal layer interposed between the first substrate and the second substrate, electrodes for applying a voltage to the liquid crystal layer, a polarizing plate provided on a side of the liquid crystal layer on which the first substrate is provided, a reflective member provided on a side of the liquid crystal layer on which the second substrate is provided, and an optical compensation member provided between the polarizing plate and the liquid crystal layer. The display device disclosed in the xe2x80x2356 patent also describes the conventional approach of using color filters to provide RGB (red, green and blue) type color display. Color filters have very low color utilization efficiency. While it allows light of intended color to pass through, those of complementary color are absorbed and thus their energy wasted. Furthermore, the provision for black matrixes also adversely affects the extent of light openings, in addition to their action to absorb light. As a result, color filters cause the transmitted light to be substantially reduced, and the need for color filters increases the manufacturing cost. With a reflective-type liquid crystal display device, since light takes two passes, the amount of intensity loss is further magnified.
Japan Open Patent App. Nos. 5-249318 and 6-308332 disclose a transmitting diffraction-type grating to replace the color filters as part of color display devices. The purpose of their design is to improve the utilization efficiency of the back light. In order to improve the proportion of first-order light and solve color positioning problems, their design requires that the back light be shined sideways. This requires a re-design of the back light assembly. The display disclosed in these Japanese patents also do not allow black matrixes, causing a great comprise in the contrast level of the displayed images.
U.S. Pat. No. 5,959,704 discloses a display device which contains a diffraction grating from which a diffracted light of the zero-th order and a diffracted light of the first order having different color light components emerge to establish color separation. The xe2x80x2704 invention also includes an array of micro-lenses which is arranged on a liquid crystal panel. The liquid crystal panel has a plurality of picture elements and each picture element includes a plurality of color display dots. The color display dots in each picture element are arranged in the vertical relationship and in the order of wavelength of the light. A green light component of diffracted light of the first order is made incident normal to the liquid, and the diffracted light of the zero-th order passes through the liquid crystal panel at a greater angle relative to the normal to the liquid crystal panel. Similar to the above-mentioned Japanese patents, the xe2x80x2704 patent uses a diffraction grating to replace the color filters, and the light was transmitted in a slanted manner. Also in both inventions, a significant amount of the photo energy (in the form of the zeroth order light) is lost. The display disclosed in the xe2x80x2704 patent further provides shadings to improve the contrast; however, this causes a portion of the incident light to be absorbed by the black shadings, and thus adversely affecting the utilization efficiency of the incoming light.
U.S. Pat. No. 5,943,109 discloses a liquid crystal display device which includes a hologram layer having predetermined patterns corresponding to patterns of a color filter. In the xe2x80x2109 patent, light inputted to the LCD device is transmitted through the hologram layer when reflected by a reflection layer out of the LCD device. The xe2x80x2109 patent uses a combination of diffraction grating and color filters to display color pixels; however, since color filters are used, most of the prior art problems still exist.
It is thus desirable to develop a color display device with improved energy utilization so as to improve visualizability and reduce power consumption, while also reducing the manufacturing cost.
The primary object of the present invention is to develop a reflective-type diffraction grating structure that will allow a color display device, such as a color crystal liquid display (LCD), to display color images without the use of color filters. More specifically, the primary object of the present invention is to develop a reflective-type diffraction grating structure that will allow a color display device to operate with improved brightness and reduced power consumption, by eliminating the need for color filters. Since color filters are typically the most expensive components of a color display device, the novel reflective-type diffraction grating structure of the present invention not only will improve the performance of the color display device, it will also substantially reduce its manufacturing cost.
The reflective-type diffraction grating structure disclosed in the present invention comprises the following key elements:
(1) a plurality of micro-lenses each having a zig-zag-shaped blazed grating surface in its bottom; and
(1) an optical coating provided on the zig-zag-shaped grating surface;
(3) a reflective member formed below the optical coating.
One of the key elements of reflective-type diffraction grating structure of the present invention is that, with the novel structure as described above, the optical coating can be easily designed so that the reflected and diffracted light will be separated into red, green, and blue components that are cyclically arranged in series and in that order, and each of the RGB color components are segregated by a black shading.
In the first preferred embodiment of the present invention, the reflective member is formed in the form of a zig-zag shaped coating matching the shape of, and parallel to, the zig-zag shaped optical coating.
The second preferred embodiment of the present invention does not have a matching zig-zag shaped reflective coating underneath the zig-zag shaped optical coating. Rather, the zig-zag shaped optical coating is formed on, but spaced apart from, a flat substrate. The space between the zig-zag shaped optical coating and the flat substrate is filled with air or an optical material such as a polymer gel having different refraction index from both the substrate and the micro-lenses. Finally, a reflective coating is formed on the bottom of the flat substrate.
With either of the preferred embodiments of the present invention, the incident light will be reflected and separated into a sequence of cyclically arranged red, green, and blue color components, each being segregated by a black shading. Each of the undesired color components can be filtered out by an appropriate light valve. Since the RGB components are separated prior to their entering the light valves, the intensity of the desired color component will not be reduced as it would when it travels through a color filter. As a result, the brightness of the color display device utilizing the novel reflective-type diffraction grating structure of the present invention will be substantially greater than that of prior art devices utilizing color filters. Furthermore, the ability of the reflective-type diffraction grating structure of the present invention, in combination with the optical coating formed on the grating surface, to generate black shadings also greatly improves the contrast level of the projected images.
The micro-lense can have a spherical or aspherical surface; its main functions are to focus the incident light beam and define the positions of the color pixels. The number of the micro-lenses is defined by the required display resolution. For example, with a required display resolution of 64xc3x97128, 8,192 micro-lenses will be provided. The design of the zig-zag shaped grating surface is to separate the incident light beam into red, green, and blue lights of approximately equal energy. The ridges of the zig-zag grating surface do not have to be a straight line.